1. Field of the Invention
The present invention relates to power conversion. More specifically, the present invention relates to a flyback converter that detects an output voltage at the primary coil without using a photo coupler and provides an essentially constant output voltage independent of the size of a load, thereby minimizing the number of additional coils used in the transformer circuit.
2. Description of the Related Art
A DC-to-DC converter is a device for transforming a DC voltage, which converts a DC input voltage to an AC voltage, and after boosting or reducing the voltage with a transformer, rectifies the AC voltage to produce a DC output voltage. DC-to-DC converters are classified as forward converters and flyback converters, depending on the construction of the transformer.
A loss of power under a light load in a converter is controlled according to treaty provisions related to regulations for reducing energy consumption. Conventionally, power consumption under a light load should be less than three watts according to the ENERGY STAR standard. As control of power consumption has been tightened in recent years, the suggested power consumption under a light load has become less than one watt, according to the BLUE ANGEL standard.
Some previously-developed flyback converters detect an output voltage using a separate detecting coil at the primary winding of the transformer to reduce power consumption. These flyback converters include the transformer for changing the DC input voltage to a predetermined level according to a winding ratio of a primary coil to a secondary coil; an output unit for rectifying an output voltage signal of the transformer into a DC voltage to drive a load; and a switch coupled to the primary coil of the transformer, which controls the on/off state of the power at the primary coil according to a control signal from a feedback unit.
In the described previously-developed flyback converters the switching time varies with the load. The heavier the load, the longer the switching time. This dependence of the switching time on the load makes controlling the switching difficult.
Other previously-developed flyback converters detect the output voltage at the detecting coil and correct the detected value. However, these flyback converters require a separate power supply circuit for controlling the switch and additional coils coupled to the transformer. Such requirements make these flyback converters more complicated and larger.
Finally, some previously-developed flyback converters incorporate a photo coupler to detect the output voltage at the secondary winding of the transformer. However, these flyback converters also require a separate power supply circuit for the photo coupler, thus reducing power efficiency.